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May 11, 2017

Dissociations Between Cognitive Deficits in Older Adults

group of happy older adultsWe have all likely had the experience of a parent or grandparent forgetting where they left their keys, or calling us by our sibling's name. Gradual decline in cognitive abilities like memory and person recognition are a part of normal aging, and problems in these two domains are common complaints in older adults.

However, although these tasks are broadly affected by aging, two recent papers show dissociations in impairments within these domains.

Eich and colleagues (online first, Behavioral Neuroscience) (PDF, 221KB) compared memory deficits at encoding and retrieval by having clinically healthy older adults perform a two-item working memory task. On each trial, four words were presented, two in red and two in blue, and participants were cued to remember either the blue or red words.

Critically, the cue was presented either before or after the word set. On lure trials the probe was a word that was part of the word set but not one of the two cued words (e.g., if red was cued, the lure would be one of the blue words). Thus, providing the correct "no" response to lures required perceptual inhibition at encoding or memory inhibition at retrieval for cues presented before or after the word set, respectively.

There was no difference in accuracy between perceptual and memory inhibition trials, but reaction times were longer on memory inhibition trials. Importantly, performance on these two trial types was differentially associated with neuromorphological changes. Perceptual inhibition was correlated with cortical thickness in the right superior parietal lobule, while memory inhibition was associated with cortical thickness in the left ventral lateral prefrontal cortex; in both cases thinner cortex was associated with less (worse) inhibition.

Notably, perceptual and memory inhibition performance were not correlated with each other, suggesting that distinct trajectories of cortical thinning in different brain regions underlie individual differences in cognitive decline in subtly different cognitive tasks.

Eich et al. examined differences in deficits arising at different stages of memory. Wiese and colleagues (online first, Journal of Experimental Psychology: Learning, Memory, and Cognition) (PDF, 501KB) examined differences in person recognition deficits for different kinds of representations: perceptual and semantic. Older and younger adults had to indicate whether a target face was famous or unfamiliar. The target face was preceded by a prime face showing the same identity, or a different, unrelated identity.

Both older and younger adults showed repetition priming in reaction times (faster performance following same-identity primes), but only younger adults showed repetition priming in accuracy as well. Although both groups showed a significant N250r, an event-related brain potential (ERP) component associated with activation of familiar face representations, the magnitude of this component was smaller in older adults.

In a subsequent experiment, primes were the written name of a highly associated famous person (e.g., Paul McCartney preceding a picture of John Lennon) or a semantically unrelated famous person. Semantic priming effects (faster performance when primes were related) did not differ between older and younger adults, and there were also no priming differences in the N400, an ERP component associated with accessing general person representations.

These results suggest a dissociation between perceptual and semantic person representations, with the former being vulnerable to age-related decline while the latter is relatively spared.

Citations

  • Eich, T. S., Razlighi, Q. R., & Stern, Y. (2017, March 23). Perceptual and Memory Inhibition Deficits in Clinically Healthy Older Adults Are Associated With Region-Specific, Doubly Dissociable Patterns of Cortical Thinning. Behavioral Neuroscience. Advance online publication. http://dx.doi.org/10.1037/bne0000194
  • Wiese, H., Komes, J., Tüttenberg, S., Leidinger, J., & Schweinberger, S. R. (2017, February 27). Age-Related Differences in Face Recognition: Neural Correlates of Repetition and Semantic Priming in Young and Older Adults. Journal of Experimental Psychology: Learning, Memory, and Cognition. Advance online publication. http://dx.doi.org/10.1037/xlm0000380